The present invention relates to a machine for the treatment of laundry, such as a dryer or washing-machine.
A known washing-machine of this kind (DE-PS 30 25 088) has the drum supported for rotation in the lye tank, while the lye tank is supported in a suitable manner on the bottom of the housing, via resilient and, in certain cases, damping supports. The drum is supported in the lye tank in the usual manner, namely in unilaterally overhung arrangement, by means of a star-shaped mounting bracket fastened undetachably to the back of the lye tank by means of a plurality of screws and fishplates. The arms of the star-shaped mounting bracket extend right to the peripheral areas of the lye tank, and may even reach around the latter, for improved solidity, as the drum, being heavily loaded with wet laundry in the operating condition of the machine, has a pronounced tendency to tilt in the hub area of the star-shaped mounting bracket where it is held by only one double bearing.
In order to provide such a mechanical arrangement with a suitable measuring system which on the one hand permits the increasing weight caused by the laundry being filled in to be recorded and evaluated automatically and which on the other hand operates with sufficient accuracy, electromechanical transducers are arranged on those parts of the star-shaped mounting brackets which are exposed to particularly pronounced stresses under the effect of the drum weight. The weight-proportional output signals supplied by these electromagnetic transducers, for example resistance strain gauges or piezoelectric transducers mounted firmly in the material of the star-shaped mounting bracket, are then transmitted to a signal-processing arrangement which is thereby enabled, for example, to evaluate the weight of the laundry filled in and to derive therefrom automatically the liquid level in the lye tank and to adapt it as required.
This publication (DE-PS 30 25 088) clearly recognizes, and explains with reference to other publications likewise dealing with the problem of recording the weight of laundry (U.S. Pat. No. 2,412,270; DE-AS 11 57 578; DE-OS 20 34 847) that sufficient accuracy, initially only with respect to the weight of the laundry, can be achieved only under certain particular conditions. The problems connected with the determination of the weight have been seen heretofore in the fact that, regardless of the type of measuring sensor used, the dead weight of the washing machine (for example 100 Kg) makes it impossible for the usual increase in weight resulting from the dry laundry (approx. 0.5 to 5 Kg) to cause effects important enough for being determined with sufficient accuracy for use in an automatic control circuit.
In setting out this theory, DE-PS 30 25 088 disregards, however, at least in part the main reason for the measuring inaccuracies namely that all measuring processes previously employed are affected by excessive frictional influences so that these, and the hysteresis produced by such frictional influences, are already sufficient reason that no exact results can be expected for the desired weight measurements. While such accuracies are already critical in determining the weight of the laundry, and the water level to be derived therefrom, they make such measurements absolutely useless if one tries to determine automatically the quantity of detergents to be added, including the quantities of fabric softeners, special detergents, and so on, and to use for this purpose automatic control circuits, including in particular minicomputers and microprocessors with corresponding storage capacities, and the like, which are currently in use today, and this although such program-controlled operation would be so very important today, especially under the aspects of environmental protection.
The same is true for the solution proposed by DE-PS 30 25 088 which does not itself even expect a better accuracy than a resolution of approx. 0.1 Kg (column 3, line 4, of the quoted patent specification).
However, such measuring inaccuracies can by no means be accepted in determining the quantities of detergents to be added, as in this case an accuracy in the gram range would be required because in the case of a predetermined detergent quantity of 20 gram an extra of only 5 gram would already mean that the prescribed quantity has been exceeded by 25%.
This is in fact the reason why all solutions proposed heretofore, including the solutions contained in DE-OS 34 13 967, GB-2 087 438 A and EP 0294014 A1, cannot achieve acceptable results in practical application although the addition of detergent quantities has been discussed in most of these publications, and program sequences and fully-automatic program controls have in fact been proposed in this connection for different operations, including the addition of detergent quantities adapted to the weight of the laundry.
It should be noted, however, in this connection that the drum-type washing-machine disclosed by DE-OS 34 13 967 only had for its purpose to ensure that the quantity of laundry filled into the washing-machine actually corresponds to the capacity of the drum, i.e. to avoid errors that may result from a mere estimation of the weight of the laundry and which may lead to the drum being either not used to full capacity or being overloaded in which case the laundry will not be cleaned as thoroughly as desired. In order to simplify the step of determining the correct quantity of laundry, the discussed publication proposes to design the upper cover plate of the washing-machine as scales comprising a display where the operator can read the correct laundry weight. Additionally, the result of the weighing operation may also be employed for varying the program of the washing-machine, for which purpose the weighing system can be coupled with the program control of the washing-machine. Except for these aspects, the publication does not propose to take other actions on the program sequence or the loading quantities.
In contrast, the arrangement of the washing-machine described by British Patent Application GB-2 087 438 A is such that liquid-filled weight sensors operating on a piezoelectric/resistive basis are mounted at the lower mounting points of supports of the drum and/or its container, such supports taking the form of hydraulic shock absorbers, for example. The output signals of the weight sensors are then transmitted to a central control circuit, for example in the form of a program-controlled microprocessor, which is said to be capable of determining the quantity of detergent to be added.
However, it is a common problem of these known "weight-determining" washing-machines, including the machines which will be described further below, that the weight sensors, regardless of their shape and design, are always arranged either in the area of the feet of the entire housing of the washing-machine, or in the area of the hydraulic suspension of the lye tank or the drums, so that the hydraulic properties of these elements are always included, or have to be included, in the measurements. In addition, and this is a very important fact, though not mentioned at any point of the publication, the influence of the supply hoses and in particular the rubber seal in the area of the door of the drum is also disregarded. However, these aspects alone already cause errors so important that--in particular if one additionally considers the frictional influences usually dependent on the prevailing temperatures and/or environmental conditions (wet or dry rubber seal of the door)--the measuring results achievable from time to time are not even sufficiently accurate to guarantee an at least approximate determination of the weight of the laundry, not to speak of the desirable metering accuracy in the gram range for the detergent quantities to be added. Finally, it has been known in connection with a washing-machine (EP 0294014 A1) to arrange weight sensors in the area of the resilient drum suspension, for supplying a microprocessor controlling the program sequence and in particular the spinning operations of the washing-machine with signals representative of dynamic weight variations resulting from imbalance conditions occurring during the spinning operation. Such signals are then compared with predetermined threshold values, and when the latter are exceeded either the spinning operation is stopped, or the acceleration of the spinning motor is interrupted for a certain period of time. Similar measures have been known also from CH-PS 651 602.
Generally, it can be said that when washing-machines are operated on the basis of minicomputers or microprocessors with controlled program sequences, the sequence control has to rely on data supplied by sensors in order to be able to control the operation of the washing-machine properly, from the first start-up and the initial introduction of the required water quantity, up to the final spinning operation. Such sensors are more and more becoming the weakest element in the processing chain, and this not only because, being actual value transmitters, they get into direct contact with the agents to be measured, but also because the ever progressing degree of electronic equipment in washing-machines permits ever higher accuracies to be achieved--a requirement which cannot, however, be met by today's actual-value transmitters. For example, it is already a problem with washing-machines to adjust the water level in the drum precisely to the level determined by the program in order to ensure on the one hand that the machine does not consume too much water--this already for environmental reasons--and on the other hand that the washing program will work as desired. The water level reached at any time is usually measured with the aid of level sensors, level pick-ups or pressure cells which are exposed to the water unilaterally. However, all these elements are connected with the disadvantage that trouble caused by dirt, furring, or the like may develop especially in the area of such elements, in particular after an extended service life of the washing-machine, and in addition the actual-value information supplied by such sensors is not always sufficiently accurate.
Further, it is desirable for the purposes of a washing-machine that the central control circuit be supplied with an initial information regarding the quantity of laundry filled into the washing-machine so that the circuit may then compute the required water quantity, based on such information, control the water supply and determine, and automatically add, the desired detergent quantities.
There is, therefore, a demand for a highly precise and, above all, robust level-measuring system for washing-machines which is capable of supplying data from which the computer installed in the washing-machine can derive the necessary metering steps automatically.
Now, it is the object of the present invention to specify a filling-quantity measuring system for a washing-machine which is particularly precise, gives reproducible measurements and which is, above all, resistant to aging and can be used universally, and which not only determines the quantity of the laundry filled in, but supplies a central control circuit with all actual values required for ensuring precise program operation and proper control of the filling levels.